L. DONCASTER 9 



number from the normal. It should be mentioned that in the males 

 of '12.25, almost constantly some of the spermatocytes are binucleate 

 or more rarely have four nuclei, and these give rise to binucleate or 

 quadrinucleate spermatozoa. I have not traced the stage at which this 

 condition arises. 



It would be premature to discuss at this early stage the meaning of 

 the observations described above. It appears probable that all the 

 females of a unisexual family have .5.5 chromosomes instead of 56. 

 Those which have only female ottspring must therefore transmit only 27 

 to each of their offspring, and one chromosome is thus not accounted 

 for. An attempt will be made when the moths hatch to find out 

 whether one chromosome is eliminated at the maturation of the egg, 

 and until that point is decided it is useless to speculate on the relation 

 of the chromosome number to sex-determination. 



There is one point of considerable theoretical importance, however, 

 which should be referred to. A gi-ossulariata female which has only 

 female offspring does not transmit the gross, factor to any of them — the 

 mother receives it fi-om her male paient, but does not transmit it to her 

 daughters, and since in this case she has no sons, she does not transmit 

 it at all. In some way, therefore, it is eliminated, perhaps most 

 probably at the maturation of the egg. She also receives 28 chromo- 

 somes from her male parent, but transmits only 27 to her offsf)ring ; 

 one chromosome must therefore be eliminated. It seems, therefore, 

 highly probable that this chromosome, which is not transmitted by the 

 female whose offspring are all females, may be the determin(5r or bearer 

 of the grossuhiriata factor. It is tempting also to suggest that this 

 chromosome is a sex-determiner — that if it is receive<l from the mother 

 and a corresponding one from the father, the zygote becomes a male, 

 and if it is received from the father only, it becomes a female. A diffi- 

 culty arLses, however, from the fact that some females at least, whose 

 mothers belonged to unisexual families, have 56 chromosomes, as has 

 been shown in the case of family '12. 25. It is probably best, therefore, 

 to reserve further consideration of this part of the subject until our 

 knowledge of the facts is more complete. 



Summary. 



1. Families consisting wholly of females have appeared in six 

 successive generations of Abraxas grossidariata ; they may consist of 

 var. lacticolor, of grossvhmata, or of equal numbers of each, according 

 to the constitution of the male parent. 



